Clarify that Box does not have inner text

CHANGELOG

@@ -1,5 +1,6 @@
 v1.4.4 (WIP)
 - Fix resize event dimensions on Windows
+- Clarify that Box does not have inner text
 
 v1.4.3 (2020-02-13)
 - Add SetFocusedFunc to TreeNode

FORK.md

@@ -5,7 +5,7 @@ requests have been merged into cview.
 # Why fork?
 
 [rivo](https://github.com/rivo), the creator and sole maintainer of tview,
-explains his reviewing and merging process in a [a GitHub comment](https://github.com/rivo/tview/pull/298#issuecomment-559373851).
+explains his reviewing and merging process in a [GitHub comment](https://github.com/rivo/tview/pull/298#issuecomment-559373851).
 
 He states that he does not have the necessary time or interest to review,
 discuss and merge pull requests:

box.go

@@ -4,14 +4,11 @@ import (
 	"github.com/gdamore/tcell"
 )
 
-// Box implements Primitive with a background and optional elements such as a
-// border and a title. Most subclasses keep their content contained in the box
-// but don't necessarily have to.
+// Box is the base Primitive for all widgets. It has a background color and
+// optional surrounding elements such as a border and a title. It does not have
+// inner text. Widgets embed Box and draw their text over it.
 //
-// Note that all classes which subclass from Box will also have access to its
-// functions.
-//
-// See https://gitlab.com/tslocum/cview/wiki/Box for an example.
+// See demos/box for an example.
 type Box struct {
 	// The position of the rect.
 	x, y, width, height int